Cryptology ePrint Archive: Report 2007/202

Provable Data Possession at Untrusted Stores

Giuseppe Ateniese and Randal Burns and Reza Curtmola and Joseph Herring and Lea Kissner and Zachary Peterson and Dawn Song

Abstract: We introduce a model for {\em provable data possession} ($\pdp$)
that allows a client that has stored data at an untrusted server to
verify that the server possesses the original data without
retrieving it. The model generates probabilistic proofs of
possession by sampling random sets of blocks from the server, which
drastically reduces I/O costs. The client maintains a constant
amount of metadata to verify the proof. The challenge/response
protocol transmits a small, constant amount of data, which minimizes
network communication. Thus, the $\pdp$ model for remote data
checking supports large data sets in widely-distributed storage
systems. Previous work offers guarantees weaker than data
possession, or requires prohibitive overhead at the server.

We present two provably-secure $\pdp$ schemes that are more
efficient than previous solutions, even when compared with schemes
that achieve weaker guarantees. In particular, the overhead at the
server is low (or even constant), as opposed to linear in the size
of the data. Experiments using our implementation verify the
practicality of $\pdp$ and reveal that the performance of $\pdp$ is
bounded by disk I/O and not by cryptographic computation.

Note: December 7, 2007: Added important references and fixed some typos.

October 12, 2007: We corrected a bug in the proof in which we erroneously assumed that the GCD of two parameters was 1 with overwhelming probability. The fix affects only the public verifiability feature of our main scheme but we now show how to achieve it by simply restricting the size of file blocks. See the Note at the end of the Introduction.